The water supply part of the water supply system is mainly composed of water pumps, motors, pipes and valves. Usually the asynchronous motor drives the water pump to rotate to supply water, and the motor and the water pump are integrated, and the stator power supply frequency is adjusted by the inverter to change the synchronous speed to achieve speed regulation, thereby changing the water flow rate of the water pump to achieve constant pressure water supply.During the operation of the system, the actual water supply pressure of the outlet main pipe network follows the set water supply pressure. The water pressure is sent to the PID module inside the inverter from the signal of the pressure sensor 4-20mA, and compared with the pressure value set by the user, and the result is converted into a frequency adjustment signal through the built-in PID calculation of the inverter to adjust the power supply of the pump motor Frequency, so as to control the pump speed.If the actual water supply pressure is lower than the set pressure, the inverter will get a positive pressure difference. This difference is converted by the inverter to PID to calculate the increase value of the inverter output frequency. This value is to reduce the actual water supply pressure and the set pressure. Difference, add this increment to the current output value of the inverter, and the value obtained is the current frequency that the inverter should output. This frequency increases the speed of the water pump unit, thereby increasing the actual water supply pressure. This process will be repeated during operation until the actual water supply pressure is equal to the set pressure. If the actual water supply pressure is higher than the set pressure during operation, the situation is just the opposite, the output frequency of the inverter will decrease, the speed of the water pump will decrease, and the actual water supply pressure will therefore decrease. Similarly, the final adjustment result is that the actual water supply pressure is equal to the set pressure.